AskDefine | Define joule

Dictionary Definition



1 a unit of electrical energy equal to the work done when a current of one ampere passes through a resistance of one ohm for one second [syn: J, watt second]
2 English physicist who established the mechanical theory of heat and discovered the first law of thermodynamics (1818-1889) [syn: James Prescott Joule]

User Contributed Dictionary



Named after the English physicist James Prescott Joule.


  • , /dʒul/, /dZul/


  1. In the International System of Units, the derived unit of energy, work and heat; the work required to exert a force of one newton for a distance of one metre. Also equal to the energy of one watt of power for a duration of one second. Symbol: J














Extensive Definition

The joule ( or /ˈdʒaʊl/) (symbol: J) is the SI unit of energy measuring heat, electricity and mechanical work. It was named after English physicist James Prescott Joule.


One joule is the work done, or energy expended, by a force of one newton moving one metre along the direction of the force. This quantity is also denoted as a newton metre with the symbol N·m. Note that torque also has the same units as work, but the quantities are not the same. In elementary units:
\, 1\, \mathrm=1\, \mathrm \cdot \mathrm
\, 1\, \mathrm=1\, \mathrm \cdot \frac
One joule is also:
  • The work required to move an electric charge of one coulomb through an electrical potential difference of one volt; or one coulomb volt, with the symbol C·V.
  • The work done to produce power of one watt continuously for one second; or one watt second (compare kilowatt hour), with the symbol W·s. Thus a kilowatt hour is 3,600,000 joules or 3.6 megajoules


A joule is the mechanical equivalent of heat meaning the number of units of work in which the unit of heat can perform. Its value was found by James Prescott Joule in experiments that showed the mechanical energy Joule's equivalent, and represented by the symbol J. The term was first introduced by Dr. Mayer of Heilbronn.


1 joule is exactly 107 ergs.
1 joule is approximately equal to:
1 joule in everyday life is approximately:
  • the energy required to lift a small apple one metre straight up.
  • the energy released when that same apple falls one meter to the ground.
  • the amount of energy, as heat, that a quiet person generates every hundredth of a second.
  • the energy required to heat one gram of dry, cool air by 1 degree Celsius.
  • one hundredth of the energy a person can get by drinking a single drop of beer.
  • the kinetic energy of an adult human moving a distance of about a handspan every second.
Units defined in terms of the joule include:
  • 1 thermochemical calorie = 4.184 J
  • 1 International Table calorie = 4.1868 J
  • 1 watt hour = 3600 J
  • 1 kilowatt hour = 3.6 J (or 3.6 MJ)
  • 1 ton TNT = 4.184 GJ
Useful to remember:
  • 1 joule = 1 newton metre = 1 watt second

SI multiples

See also


joule in Afrikaans: Joule
joule in Arabic: جول
joule in Asturian: Xuliu (unidá)
joule in Bengali: জুল
joule in Belarusian: Джоўль
joule in Belarusian (Tarashkevitsa): Джоўль
joule in Bosnian: Džul
joule in Bulgarian: Джаул
joule in Catalan: Joule
joule in Czech: Joule
joule in Danish: Joule
joule in German: Joule
joule in Estonian: Džaul
joule in Modern Greek (1453-): Τζάουλ (μονάδα μέτρησης)
joule in Spanish: Julio (unidad)
joule in Esperanto: Ĵulo
joule in Basque: Joule (unitatea)
joule in Persian: ژول
joule in French: Joule
joule in Scottish Gaelic: Joule
joule in Galician: Joule (unidade)
joule in Korean: 줄 (단위)
joule in Croatian: Džul
joule in Indonesian: Joule
joule in Icelandic: Júl
joule in Italian: Joule
joule in Hebrew: ג'ול
joule in Swahili (macrolanguage): Jouli
joule in Latin: Joulium
joule in Latvian: Džouls
joule in Lithuanian: Džaulis
joule in Hungarian: Joule
joule in Malay (macrolanguage): Joule
joule in Dutch: Joule
joule in Japanese: ジュール
joule in Norwegian: Joule
joule in Norwegian Nynorsk: Joule
joule in Occitan (post 1500): Joule
joule in Polish: Dżul
joule in Portuguese: Joule
joule in Kölsch: Joule (Mohß)
joule in Romanian: Joule
joule in Russian: Джоуль
joule in Simple English: Joule
joule in Slovak: Joule
joule in Slovenian: Džul
joule in Serbian: Џул
joule in Finnish: Joule
joule in Swedish: Joule
joule in Thai: จูล
joule in Vietnamese: Joule
joule in Turkish: Joule (birim)
joule in Ukrainian: Джоуль
joule in Urdu: جاؤل
joule in Venetian: Joule
joule in Chinese: 焦耳
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